BUILD: Automate the list of data files to be distributed
The attached patch prepares some variables that contain the theme files and the engine data files that should be distributed together with the binaries. Maybe these could be merged in a common "DIST_DATAFILES" variable which also contains pred.dic, since all those files seem to be copied to the same directory.
The case of the engine data files is specially interesting because it just lists the data files needed by the built engines. For example, igor.tbl won't be on the list if configured with the default options.
I've also tried to upgrade ports.mk so that these new variables replace the old behavior.
Ticket imported from: #1862888. Ticket imported from: patches/873.